Police have released images of five men who were in the crowd during the Hillsborough disaster and could have “important information” .
Operation Resolve, the criminal investigation into the disaster, is launching its Gate C appeal.
Ninety-six fans were fatally injured at the 1989 FA Cup semi-final.
Detectives said the men in the photos could help build a “clearer picture” about the events leading up to the opening of Exit Gate C at 14:52.
Hundreds of statements have been taken from fans who approached the 23 turnstiles that could be accessed from the Leppings Lane end of the stadium.
However, Operation Resolve has been unable to trace a small number of people who could be seen at key times.
This inquiry is separate to the ongoing witness appeal trying to find fans who helped people who died.
New inquests into the disaster are being held in Warrington, Cheshire.
Assistant Commissioner Jon Stoddart said: “I am asking these men or anyone that knows them to come forward. If this is you please call us.
“The aim of this appeal is to find answers and continue to build a clearer picture about events of the day. All information provided will be thoroughly researched by our team.”
He added: “My message to the people themselves is clear: we just want to know what you saw or heard. We believe the five men pictured may have important information concerning the events outside Exit Gate C, and this remains an investigative priority for us.
“We want to have as detailed an understanding as possible of the events outside the 23 turnstiles at the Leppings Lane end of the ground as well as the three exit gates, A, B and C, each of which were opened before kick-off.”